1. Field of the Invention
The present invention relates to a mobile communication method for transmitting a first location registration related signal addressed to the first exchange to a radio network controller, so as to perform location registration to a first exchange and a second exchange, in the case where a mobile station operates in a “Network Operation Mode I”.
Also, the present invention relates to a mobile station which can be used in the mobile communication method.
2. Description of the Related Art
Conventionally, a mobile communication system, which provides a “Domain Combined Mobility Management (MM) procedure”, is known. This type of mobile communication system will be described by referring to FIGS. 1A and 1B.
In the mobile communication system, a radio network controller RNC is configured to notify a network operation mode to a mobile station UE via a base station BS.
Here, the network operation mode indicates a method of performing the location registration to an exchange for a packet switched service (first exchange) SGSN (serving GPRS support node) and an exchange for a circuit switched service (second exchange) MSC/VLR (mobile service switching center/visitor location register).
When operating in the Network Operation Mode I, as shown in FIG. 1A, the mobile station UE is configured to transmit a first location registration related signal addressed to the SGSN to the radio network controller RNC via the base station BS, so as to perform the location registration to both the SGSN and the MSC/VLR.
To be more specific, first, the radio network controller RNC transfers the first location registration related signal transmitted from the mobile station UE via the base station BS, to the SGSN.
Second, the SGSN performs the location registration of the mobile station UE in use of the first location registration related signal transferred from the radio network controller RNC, and transfers the first location registration related signal to the MSC/VLR via GsIF.
Third, the MSC/VLR performs the location registration of the mobile station UE in use of the first location registration related signal transferred from the SGSN.
In this case, the mobile station UE can perform the location registration to both the SGSN and the MSC/VLR, only by transmitting the first location registration related signal addressed to the SGSN.
Therefore, the mobile station UE does not need to transmit the first and second location registration related signals separately to the SGSN and the MSC/VLR, so that the traffic in the radio communication area can be reduced.
In the above described mobile communication system, the mobile station UE is configured to transmit one of the first service related signal addressed to the SGSN or a second service related signal addressed to the MSC/VLR to the radio network controller RNC, so as to use predetermined services such as a short message service or a global positioning service.
However, in the mobile communication system providing the conventional “Domain Combined MM procedure”, the mobile station UE which operates in the Network Operation Mode I cannot perform the location registration to either the SGSN or the MSC/VLR, when congestion or failure occurs in the SGSN.
To be more specific, as shown in FIG. 1B, when congestion or failure occurs in the SGSN in step S1, the SGSN transmits a state signal to the radio network controller RNC in order to notify the occurrence of the congestion or the failure in step S2.
In step S3, the radio network controller RNC broadcasts an access restriction signal which restricts accesses to the SGSN (a packet switched service domain).
In step S4, the mobile station UE stops transmitting the location registration related signals to the SGSN in accordance with the received access restriction signal.
When operating in the Network Operation Mode I, the mobile station UE performs the location registration to the MSC/VLR by using the first location registration related signal addressed to the SGSN. Therefore, in this case, the mobile station UE cannot perform the location registration to the MSC/VLR (circuit switched service domain) which is originally available.
Further, in the above described mobile communication system, there is a problem in that the mobile station UE, which has received the access restriction signal when the congestion or the failure in the SGSN occurs, cannot use predetermined services provided by the MSC/VLR, by automatically switching to transmit the second service related signal addressed to the MSC/VLR to the radio network controller RNC.